Inkjet recording methods enable simple and inexpensive image formation, and therefore have been widely used. Examples of inks to be used for the inkjet recording methods include an actinic radiation-curable inkjet ink. As for the actinic radiation-curable inkjet ink, most part of the ink component is cured due to the irradiation with actinic radiation such as ultraviolet rays and thus is dried more easily than a solvent-based ink composition, and an image formed with the ink is hard to bleed. Therefore, the actinic radiation-curable inkjet ink has an advantage of enabling images to be formed on various recording media.
Image formation by means of inkjet recording method is typically performed by discharging an ink supplied from an ink tank of an inkjet recording apparatus from a recording head. However, when the ink contains air bubbles in supplying the ink to the recording head, the flow resistance is increased, which may cause discharge deficiency of the ink.
In order to remove such air bubbles, for example, methods have been proposed such as a method of degassing an inkjet ink by allowing it to flow through a hollow fiber degassing module for degassing before filling the inkjet ink into a cartridge (e.g., Patent Literature (hereinafter, referred to as “PTL”) 1); and a method of degassing an inkjet ink immediately before being discharged with a degassing filter provided between an ink tank of an inkjet recording apparatus and a nozzle of a recording head (e.g., PTL 2).
Further, it is known that an actinic radiation-curable inkjet ink, in particular, an actinic radiation-curable inkjet ink containing a wax contains more dissolved oxygen than an aqueous ink, and has higher viscosity than a solvent-based ink, thus making the discharge stability likely to be lowered (e.g., PTL 3). To address such problems, a method in which an actinic radiation-curable inkjet ink immediately before being discharged is heated inside a recording head to reduce the viscosity of the ink, or other methods are proposed (e.g., PTL 4).